A flaw in Microsoft's Outlook Express has left users vulnerable to malicious code embedded into vcards - virtual business cards - which are used to sign many business emails.
Hackers can crash target machines or, more seriously, run code on the user's machine if they open a vcard.
According to Microsoft's security advisor, attackers are limited only by user preferences as to what code they can execute via the vcards.
Users can work around the issue by simply not opening vcards. The flaw affects Outlook 97, Outlook 2000, Outlook Express 5.01 and Outlook Express 5.5.
Microsoft has made a patch available here for users to download.
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